FUNDAMENTAL AND PRACTICAL ASPECTS OF LANCE DESIGN FOR POWDER INJECTION PROCESSES.

Most lance designs and the associated operating conditions have been developed empirically, and are not necessarily optimized. In this paper, an attempt is made to apply fundamental transport phenomena to obtain a better understanding of powder injection processes. The fluid dynamics in the vicinity of the lance will be reviewed, and it will be shown that mathematical models can predict the flow regimes, such as bubbling and jetting. Heat transfer processes during injection have been studied. The results have important implications for gas and particle temperatures in the lance, clogging phenomena and lance life. From this understanding of the heat transfer phenomena, in the lance and ascending plume, the degree of particle-liquid contact can be estimated from bath cooling rates. Based on measurements in liquid lead, it was found that particle- liquid contact can be increased by angled injection and by gas-evolving compounds (i. e. the simulation of magnesium, calcium and limestone injection in ferrous systems). The implications of these findings on reagent utilization and reaction rates are discussed. The effect that powder injection has on vessel mixing times is shown to be negligible except when the particles carry the gas deeper into the melt than without particle injection.